1. Field of the Invention
The present invention relates to the production of solutions of stannous salts, and more especially, to the production of aqueous solutions of stannous fluoborate and stannous sulfate.
2. Description of the Prior Art:
Certain solutions of stannous salts, such as the fluoborate and sulfate, are especially industrially useful, in particular for the electrolytic deposition of metallic tin.
The preparation of these stannous salts is currently carried out by processes entailing successive transformations of metallic tin into the chloride thereof by the action of hydrochloric acid in the presence of an oxidizing agent, e.g., chlorine, then into the oxide SnO by treating the stannous chloride with a solution of sodium carbonate, the stannous oxide ultimately being dissolved in fluoboric or sulfuric acid. These processes have the disadvantage of including different successive operations involving product losses and resulting in products which may have high contents of stannic tin.
It is also known to this art that some stannous salts can be prepared by simple attack of the metallic tin with the corresponding acid. The disadvantage of these processes are the slow kinetics and the slow rate provided thereby. It is furthermore known that the speed of reaction can be considerably improved by adding oxygen to the reaction medium. This, however, requires the use of a second reactor in which the stannic tin formed is reduced by passing the tin solution over the metallic tin in a reducing or inert atmosphere. See U.S. Pat. No. 3,432,256.
Also known to this art are a number of electrolytic processes for the production of stannous salts. Compare U.S. Pat. Nos. 3,300,397 and 3,795,595; French patent No. 2,338,900. Such processes are difficult to implement, as a practical matter.